1. Field of the Invention
This invention relates to a mobile telephone system, and more particularly to a digital portable telephone apparatus with a holding function and a VOX function and a method for transmitting a holding tone of the apparatus.
2. Description of the Related Art
FIG. 1 is a block diagram showing the construction of a conventional example of a digital portable telephone apparatus which realizes a holding condition of speech.
Key inputting section 1 is used for a speaker to depress operation keys to input a destination number or various function inputs. Microphone 3 converts the inputted sound into sound signal Sv, and ascending sound signal processing section 4 converts sound signal Sv into sound data TX. Transmission section 6 generates transmission signal STX from inputted sound data TX, and antenna 7 radiates transmission signal STX. Meanwhile, reception section 10 converts reception signal RTX inputted thereto by way of antenna 7 into sound data RX, and descending sound signal processing section 8 converts sound data RX into sound signal Sv. Loudspeaker 9 converts inputted sound signal Sv into sound and outputs the sound. Holding tone generation section 11 generates holding tone data Sk upon holding, and change-over switch 12 changes ascending and descending sound signals Sv for holding tone data Sk and vice versa. Control section 2 controls the components described above.
Next, operation of the conventional example of FIG. 1 is described. Upon ordinary conversation, sound signal Sv from microphone 3 is converted into sound data TX by ascending sound signal processing section 4 and transmitted as transmission signal STX from antenna 7 by way of transmission section 6. Meanwhile, reception signal RTX fetched by antenna 7 is sent to and converted by reception section 10 into sound data RX. Sound data RX are converted into sound signal Sv by descending sound signal processing section 8 and outputted by way of loudspeaker 9.
On the other hand, in a holding condition, the speaker makes change-over switch 12 to change over from the output of microphone 3 to the output of holding tone generation section 11. Consequently, holding tone data Sk successively pass ascending sound signal processing section 4 and transmission section 6 and are transmitted from antenna 7. Simultaneously, descending sound signal Sv is changed over to the output of holding tone generation section 11 by change-over switch 12, so that descending holding tone is outputted from loudspeaker 9.
FIG. 2 illustrates timings at which control section 2 controls ascending sound signal processing section 4 and transmission section 6 to change over from holding tone data Sk, which is an audio signal, to ascending sound data TX. In particular, for every sound sampling time Tn (n=1, 2, 3, . . . ) of a fixed duration, holding tone data Sk is sampled and converted into sound data TXn (n=1, 2, 3, . . . ) by ascending sound signal processing section 4. Each two same sound data thereof are interleaved and successively sent out as ascending sound data Tx to transmission section 6. Transmission section 6 generates transmission signal STX from ascending sound data TX and transmits transmission signal STX.
In the digital portable telephone apparatus of the conventional example described above, in a holding condition, holding tone data Sk is successively converted into ascending sound data TX for each sound sampling time and continuously transmitted. Therefore, even if holding tone data Sk is same over a plurality of sound sampling times, every holding tone data Sk is successively converted into ascending sound data TX and continuously transmitted. Accordingly, it is difficult to reduce the transmission time upon holding and reduce the power dissipation.